Anterior cruciate ligament (ACL) injury is prevalent and often leads to instability, quadriceps muscle weakness and osteoarthritis. (OA) Many of those with chronic ACL deficiency have evidence of knee OA years after ACL rupture. Weakness and instability experienced by those who do not compensate well for ACL deficiency (non-copers) independently lead to compensation strategies that could precipitate or worsen knee OA. These poor compensation strategies do not uniformly resolve after surgical reconstruction and those who undergo reconstruction also have an increased risk of developing knee OA. The overall goal of this work is to determine whether effective rehabilitation programs to dynamically stabilize the knee improve outcome and reduce maladaptations after ACL reconstruction in a population at great risk for the development of knee OA. Eighty individuals with ACL rupture who are scheduled for surgery will be randomly assigned to a group that includes a form of neuromuscular training called perturbation training, or a standard group. They will be evaluated before and after surgery using motion analysis and radiography, in vivo measures of kinematics, kinetics, tibial translation and EMG based models of joint compression will be used for comparison. This randomized trial is designed to demonstrate that, after preoperative rehabilitation that includes perturbation training, non-copers will: 1) demonstrate movement and muscle firing patterns that are characteristic of those with dynamic stability, 2) these changes will persist after reconstruction and 3) training induced changes in movement and muscle firing patterns will result in better functional outcomes after reconstruction. The information derived from this project will provide valuable insight into the management of the approximately 100,000 Americans who rupture their ACL's each year and undergo reconstructive surgery. More importantly, if pre-operative perturbation training can facilitate both improved patient outcomes and a reduction in maladaptions following reconstructive ACL surgery, these findings may have applications for individuals with an extensive range of knee injuries.